This invention generally relates to a gas turbine engine, and more particularly to a turbofan gas turbine engine having a ducted inner fixed structure for modulating a discharge airflow cross-sectional area of the gas turbine engine.
In an aircraft gas turbine engine, such as a turbofan engine, air is pressurized in a compressor, and mixed with fuel and burned in a combustor for generating hot combustion gases. The hot combustion gases flow downstream through turbine stages that extract energy from the gases. A high pressure turbine powers the compressor, while a low pressure turbine powers a fan section disposed upstream of the compressor.
Combustion gases are discharged from the turbofan engine through a core exhaust nozzle, and fan air is discharged through an annular fan exhaust nozzle defined at least partially by a fan nacelle surrounding the core engine. A significant amount of propulsion thrust is provided by the pressurized fan air which is discharged through the fan exhaust nozzle. The combustion gases are discharged through the core exhaust nozzle to provide additional thrust.
A significant amount of the air pressurized by the fan section bypasses the engine for generating propulsion thrust in turbofan engines. High bypass turbofans typically require large diameter fans to achieve adequate turbofan engine efficiency. Therefore, the nacelle of the turbofan engine must be large enough to support the large diameter fan of the turbofan engine. Disadvantageously, the relatively large size of the nacelle results in increased weight, noise and drag that may offset the propulsive efficiency achieved by the high bypass turbofan engine.
It is known in the field of aircraft gas turbine engines that the performance of the turbofan engine varies during diverse flight conditions experienced by the aircraft. Typical turbofan engines are designed to achieve maximum performance during normal cruise operation of the aircraft. Therefore, when combined with the necessity of a relatively large nacelle size, increased noise and decreased efficiency may be experienced by the aircraft at non-cruise operating conditions such as take-off, landing, cruise maneuver and the like.
Accordingly, it is desirable to provide a turbofan engine having a discharge airflow cross-sectional area that may be modulated to achieve noise reductions and improved safety and efficiency of the gas turbine engine in a relatively inexpensive and non-complex manner.